1. Technical Field
The present invention relates to an imaging device and, in particular, to technology that reduces occurrences of malfunctions due to damage to data relating to operation control of imaging devices in inferior surroundings.
2. Related Art
Recently, machine vision (sensing) that uses imaging devices (e.g., cameras) have been put in practical use. For example, a camera is mounted on a mobile object such as an automobile, and a variety of controls of the mobile object are performed using image data captured by the camera. When a camera is mounted on a mobile object such as an automobile, it is highly likely that the camera is operated in inferior surroundings in which external noise such as static electricity, thunderbolt and the like are present. Also, the camera may not always be operated under stable conditions, because it is battery-driven and therefore the power supply condition would likely become unstable due to fluctuation in the power supply and noise.
In particular, an automobile is equipped with many sources that generate strong electromagnetic waves, such as, generators, electrical components for the ignition system and the like. Influence of electromagnetic waves could lead to malfunctions. In order to prevent such malfunctions, electronic devices are surrounded by electromagnetic shields to prevent mixing of such electromagnetic waves.
A typical composition of a camera is shown in FIG. 12. The camera shown as an example in FIG. 12 is configured with a microcomputer that governs the overall operation of the camera, a ROM (a nonvolatile memory) that stores a program for the microcomputer, an imaging lens, an imaging element, a digital signal processor (DSP) that processes captured image signals from the imaging element and outputs image signals for display to a host system, and a power supply circuit that converts a power supply from a battery device to a power supply voltage for each device.
A serial communication signal in FIG. 12 normally controls electronic shutter speeds of the imaging element. The host system may be, for example, a navigation system, an ECU or the like mounted on an automobile. Image signals for display may be transmitted to the host system, for example, as analog video signals, video signals of digital differential pairs, or optical video signals. It is noted that the imaging element in the camera needs to take in external light, and therefore cannot be covered by an electromagnetic shield that shuts off electromagnetic wave which is external noise. Therefore, the imaging device would likely be affected by external noise. Also, it is likely that power supply noise generated by the battery device cannot be completely removed by the power supply circuit within the imaging device.
More specifically, when a CMOS image sensor that can switch its operation with registers is used for the vehicle-mounted camera, the register values may suddenly change due to the aforementioned noise, which would possibly cause an abnormal state (a hang up), and an operational abnormality. Such an operational abnormality could lead to a very dangerous situation, when the driver is performing a driving operation while watching the captured image, or the host system shown in FIG. 12 is controlling the vehicle using the captured image. Furthermore, not only the imaging element, but also the microcomputer of the camera may malfunction. When the microcomputer has a malfunction, the entire system would be placed in an abnormal state. In this connection, for example, JP-A-2009-111546 describes an imaging device as a technology to prevent malfunctions of a camera.
The technology described in JP-A-2009-111546 may prevent malfunctions of a camera for a local failure, but may find it difficult to prevent or reduce malfunctions which may be caused by damage to control information stored in the registers of the camera due to electromagnetic waves, noise and the like.